For example, in a supercritical fluid chromatograph, a sample is injected by a loop injection method (see, for example, Japanese Patent No. 4675406 herein incorporated by reference). In a loop injection method, a sample is introduced into a sample loop, then a flow path is switched to supply a mobile phase in the sample loop, so that the sample in the sample loop can be flowed into a column together with the mobile phase. At this time, using a flow path switching unit such as a six-way valve, the flow path is switched between an introduction state for introducing the sample into the sample loop and an analysis state for flowing the mobile phase to a column via the sample loop.
In a loop injection mechanism that supplies a sample to a column with such a loop injection method, when cleaning the inside of the sample loop, the flow path is switched to a cleaning state in which a cleaning solution is flowed into the sample loop. By washing the inside of the sample loop in this cleaning state and then switching the flow path to the analysis state again, it is possible to completely remove the sample in the sample loop to thereby prevent occurrence of a phenomenon (so-called carry over) in which a peak based on the previous sample component appears at the next analysis.
In the case of automatically switching the flow path, a plurality of control commands to be given to a control unit is preset by a user, and the flow path is switched by sequentially executing the preset plurality of control commands by the control unit. In a conventional loop injection mechanism, such setting of control commands is performed by a user by arbitrarily selecting and combining a plurality of control commands.